The invention relates to a unidirectional drive assembly of the type that is operable to drive an output gear in a single direction of rotation responsive to rotation of an input drive gear in either a forward or a reverse direction and, more particularly, the invention relates to such a unidirectional drive assembly that is well suited for use in driving a watthour meter register which must combine the features of compact assembly, reliable operation, and highly accurate throughput with low manufacturing cost.
The use of various types of unidirectional registers to record power measured by electric watthour meters has been a common practice for many years. Such registers were initially developed to prevent misuse of the meters that might cause them to record an improperly low rate of power consumption. As is generally well-known, a conventional watthour meter of the induction type may be made to rotate in a reverse direction simply by reversing the potential applied to the meter. For example, if a conventional watthour meter is removed from its socket and simply inverted then re-inserted into the socket, the meter will rotate in a reverse direction and cause the power indicated on its register to be reduced. In order to prevent such cases of meter misuse, unidirectional registers were developed that operate to cause the meter register indicators to rotate in an up-scale direction responsive to either a forward or reverse direction of rotation of the meter register drive gear.
Although unidirectional registers have become relatively common, they typically are still relatively complex assemblies that are subject to various shortcomings. For example, they tend to introduce inaccuracies into the registered output due to lags in the shift mechanisms employed. Moreover, their complex nature results in undesired manufacturing costs as well as tending to penalize the meter system by requiring undesirably large amounts of power to drive such mechanisms. In addition, such prior art systems have characteristically required a significant portion of the space available within a standard meter housing in order to accommodate their complex gear trains. In such an environment it is desirable to simplify assemblies whenever feasible in order to conserve space.
It is also virtually imperative that a unidirectional register be maintenance free and, more specifically, such registers should not be subject to jamming or locking during either the performance of their shifting functions or during normal indicator driving operation. Two common causes of such locking in prior art unidirectional registers has been found to be associated with both gear topping during a register shifting operation in response to a reversal of the input drive gear, and to gear bottoming within the shifting gear train after a reversal in direction has occurred. Such shortcomings have, of course, been recognized heretofore and various precision adjustment means are frequently provided to avoid failures or jamming due to gear bottoming or topping, but in known prior art unidirectional register assemblies such mechanisms normally are time consumming to adjust and tend to be the source of further maintenance problems and meter register inaccuracy problems during normal operation thereof.